FIG. 1 (Prior Art) is a perspective diagram of one type of conventional network switching device that operates in accordance with one particular SDN (Software-Defined Networking) protocol called “OpenFlow”. OpenFlow provides a standard way to control the flow tables in the various switches of a network, even though the underlying hardware of the various switches may be different. A description of an OpenFlow compliant switch, the OpenFlow protocol, and the OpenFlow protocol stack is available from the OpenFlow Consortium at http://openflow.org and available as the OpenFlow Switch Specification, version 1.1.0, Implemented (Feb. 28, 2011). The device 1 includes a control plane blade 2, and numerous SDN switch blades 3. A blade is a printed circuit board assembly. All these printed circuit board blades are disposed in an enclosure or housing 4 as shown. The SDN switch blades 3 may operate together as a private network within the housing 4. How packets are forwarded from one switch to another within the device is defined by flow tables in the switches, and these flow tables are in turn configured and maintained by the control plane blade 2. Once packets of a flow are being switched by a switch within the device 1, the flow entry that controls how that flow is switched within the housing is not changed.
FIG. 2 (Prior Art) is a simplified block diagram of another type of conventional OpenFlow switching device 5 referred to as a top-of-rack (ToR) switch. Device 5 involves an x86-architecture-based control plane portion 6 and a switching portion 7, where the switching portion involves a fabric of integrated circuits available from Broadcom Corporation, 5300 California Avenue, Irvine, Calif. 92617. The control portion 6 executes an OpenFlow protocol stack and receives and outputs OpenFlow messages in accordance with the OpenFlow protocol. A relatively small percentage of the network traffic flow (for example, one percent) through the device is received onto the switching portion and is then passed up to the control portion 6 so that the control portion can determine how that traffic should be switched. When the determination is made, the switching portion outputs the traffic as dictated by the control portion. A relatively large percentage of network traffic flow (for example, ninety-nine percent) through the device 5, however, passes into the switching portion 7 and is switched out of the switching portion 7 without having to be passed up to the control portion 6. As in the case of the device OpenFlow device of FIG. 1, flow entries in the flow tables in the switching portion that determine how flows of packets are switched by the switching portion 7 are not changed once packets of such flows have started passing through the device.